Vinyl chloride resin whose hardness can be easily adjusted by adding plasticizers, can be used for various uses. In particular, since hard vinyl chloride resin compositions having no plasticizer, or semi-hard vinyl chloride resin compositions having only a small amount of plasticizer have excellent rigidity, they are widely used for building materials or the like. Therefore, hard vinyl chloride resin compositions having no plasticizer and semi-hard vinyl chloride resin compositions having only a small amount of plasticizer require more advanced performance not only in working at high temperatures and pressures but also in heat stability and weather resistance as molded articles.
In the past, hard transparent molded articles obtained from hard vinyl chloride resin compositions have been used for a wide range of products such as cases, industrial boards, decorative boards, film and sheets which require glass-like transparent products. On the contrary, vinyl chloride resin is generally insufficient in stability against light and heat. Therefore, coloring and deterioration of physical properties occur easily since degradation caused mainly by de-hydrogen halide occurs when heat molding is carried out or when the products are used, which are known as disadvantages. In order to improve these disadvantages, attempts have been conventionally made wherein various stabilizers such as organic acid metallic salt, organic tin compound, organic phosphite compound, epoxy compound, β-diketone compound, antioxidant and ultraviolet absorber are blended to improve the stability of vinyl chloride resin.
Conventionally, heavy metal stabilizers such as lead and cadmium have been used from a superiority of cost performance or the like as the above stabilizer. Recently the interest in environmental problems has been growing, therefore, the toxicity and effects of the heavy metal or the like against the environment have come to problems and there has been a tendency to use barium-zinc composite stabilizers. However, in recent years the effects of barium against the environment have started to cause concern. Therefore, the replacement to further lower-toxic calcium-zinc, magnesium-zinc or calcium-magnesium-zinc composite stabilizers is required.
From such viewpoints, a method for adding organic acid calcium salt, organic acid zinc salt, basic phosphorous acid salt and hydrotalcite compounds (Patent document 1), and a method for adding organic acid alkaline earth metallic salt, organic acid zinc salt, basic zinc phosphate and hydrotalcite compounds (Patent document 2) were proposed. However, even though these compounds are used in combination, the performances of heat resistance or the like were insufficient. In addition, there was no description concerning transparency in these patent documents at all, and there was no suggestion of improvement in transparency at all.
Furthermore, vinyl chloride foaming resin compositions for foaming molded products wherein an inorganic filler, a zinc compound, a zinc-modified hydrotalcite compound and a thermal decomposition type organic foaming agent are added (Patent document 3), and polyvinyl chloride resin compositions for food wrapping wherein a adipic acid ester plasticizer, a calcium salt of organic carboxyl acid and a zinc-modified hydrotalcite compound are blended (Patent document 4) are disclosed. However, since there are no descriptions concerning transparency at all in any of these documents, any knowledge concerning the improvement of transparency can be obtained from these documents.
In addition, tin stabilizers are proposed as a stabilizer which can enhance transparency (Patent documents 5 and 6). However, tin is also not preferable from the viewpoints of effects on the environment and toxicity. Moreover, a lot of tin stabilizers are liquid. Therefore, in cases where these are used, not only lubricating properties of molten resin decrease during mold-working, but also the thermal deformation temperature of molded object (a softening point) drops, which was a problem.